Messages in this thread | | | From | manfreds@colorful ... | Subject | Re: [PATCH] i386 rwlock bug? | Date | Fri, 20 Aug 1999 13:50:58 -0400 (EDT) |
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> > Bug or feature? > I've modified this to leave the high bit on while waiting for the > readers to go away, thus making the high bit a 'write lock pending' > bit. This makes sure that while the writer is waiting for the write > lock no more readers can come in. I think this is a feature: rw-locks can be use partially in interrupts: * write only from outside interrupts * read from everywhere
if a writer spins (interupts are enabled), then an interrupt occurs, then you have a dead-lock.
WinNT has special "acquire_shared_starve_writer()"-calls but I don't think this is required.
> Does anyone consider the current behaviour a feature? Are there > arguments against my patch? Agreed, there isn't always much lock > contention, so you can say "Leave it this way." but I use rwlocks in > 'heavy contention' situations and (for example) with 10 readers and 1 > writer the writer never acquires the write lock without this patch. add your code as a "rw-don't-starve-lock", but I think the normal rw_lock must starve writers.
-- Manfred
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